<!DOCTYPE html>

<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title></title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="">
    </head>
    <body>
      
        <script>
            
         function func(){
            let i =4;
            var i =1;
         }                      
         func();
         //无法运行
//let不允许在相同作用域内，重复申明同一个变量
        </script>
    </body>
</html>